1. Field of the Invention
The present invention relates to a flexible disk drive device (hereinafter simply called an FDD), and more specifically relates to an FDD which eliminates adjustment of the pulse width of an index signal which is required when a rotating speed of the FDD is afterward switched to a new rotating speed, such as 300, 360 and 600 rpm.
2. Description of Related Art
FIG. 4 is a view for explaining a three-phase motor control circuit including a conventional index signal generating circuit for an FDD.
The control circuit, which serves as a motor drive control circuit for driving a motor 1 and comprises a sensing circuit 2, an input amplifying circuit 3, a drive signal producing circuit 4 and a drive circuit, further comprises a speed selection circuit 6 and an index signal generating circuit 7.
The motor 1 comprises three coils to which flow drive currents having phases shifted by about 120.degree. each other, whereby the motor 1 is rotated.
The sensing circuit 2 is constituted by three Hall elements as its major components, and senses the rotating phase of the motor 1 and outputs a phase detection signal having a sinusoidal waveform or the like in the form of a voltage signal (a current signal is also acceptable). The respective Hall elements are always kept in an operative condition by a current flowing from a power source line Vcc to the ground line GND via a resistor.
The input amplifying circuit 3 is constituted by three major components differential amplifiers for receiving the respective detection signals. The amplifying circuit 3, amplifies the detection signals and outputs the same to the drive signal producing circuit 4. The drive signal producing circuit 4 receives the three amplified signals from the differential amplifiers, produces three signals based upon the received signals, the phases of which are advanced by e.g. 30.degree. with respect to the respective detection signals and shifted by 120.degree. with respect to each other, and outputs the same to the power drive circuit 5. The power drive circuit 5 is constituted by three power amplifying circuits which outputs drive currents which correspond to the waveforms of the respective drive signals outputted from the drive signal producing circuit 4, and outputs these drive currents to the coils in the motor 1.
In these kinds of motor control circuits, the motor 1, the sensing circuit 2, the input amplifying circuit 3 the drive signal producing circuit 4 and the power drive circuit 5 forms a feedback loop. Namely, the sensing circuit 2 generates the respective detection signals corresponding to the rotating phase of the motor 1 dependent upon the rotating condition of the motor 1, and the three-phase motor 1 is driven in a three-phase full wave by the drive signals having phases advancing by e.g. 30.degree. with respect to the respective corresponding detection signals and having waveforms corresponding to the respective detection signals. In response to the motor drive, the sensing circuit 2 detects detection signals dependent upon the rotating condition of the motor 1, whereby the motor 1 is controlled to rotate at a predetermined constant rotating speed under a steady state condition.
Now, rotating speeds such as 300, 360 and 600 rpm are currently employed for an FDD, therefore motor control circuits for an FDD are designed to allow selection of these rotating speeds from the outside. For this reason, the drive signal producing circuit 4 receives a speed selection signal A, which is set in response to the manipulation from the outside as illustrated in the drawing. When the speed selection signal A is received, the amplitude of the drive signals is varied dependent upon the condition of the selection signal A, and the motor 1 is driven to control the rotating speed to settle at the controlled rotating speed represented by the condition.
Another motor control circuit different from the one explained above is known in which a frequency generating coil (hereinafter simply called an FG coil) is provided at the motor side in order to detect the rotating speed of the motor 1. The detection signals are received by a servo circuit and the servo circuit drives the power drive circuit 5. The servo circuit in place of the drive signal producing circuit 4 further receives the speed selection signal A and varies the amplification rate of the power drive circuit 5 based upon the received signal A to thereby vary the rotating speed of the motor 1.
Still another motor control circuit different from the one explained above is also known in which similar detection signals are received. In response to the received detection signals, rectangular waveform signals are generated, and then a phase error signal is generated by comparing the phase of the generated rectangular waveform signals with a reference. The motor 1 is driven in order that the phase of the detection signals coincides with the reference phase; i.e. the motor 1 is controlled to rotate at a rotating speed corresponding to the reference phase.
In each case switching the switching control of the motor rotating speed is performed in the same manner through the manipulation from the outside. Therefore the operation of the conventional motor control circuit will be explained with reference to the example shown in FIG. 4.
The speed selection circuit 6 is constituted by a switching circuit 6a which permits manipulation from the outside and a selection signal generating circuit 6b. The selection signal generating circuit 6b outputs a speed selection signal A of "1" or high level (hereinafter simply indicated as "H"), or "0" or low level (hereinafter simply indicated as "L") depending upon the set condition of the switching circuit 6a. The speed selection signal A is received by the drive signal producing circuit 4 and the motor drive control circuit performs a control for maintaining the rotating speed of the motor 1 at respective predetermined rotating speeds dependent upon the conditions or the values of the speed selection signal A.
The index signal generating circuit 7 functions to generate an index signal in synchronism with the rotation of the motor and is constituted by such as an externally equipped charging circuit 7a, a flip-flop 7b, a discharging circuit 7c, a comparator 7d, a reference voltage setting circuit 7e and a reference voltage generating circuit 7f. The circuits in the drawing surrounded by dashed lines are constituted by one or a plurality of ICs, and the Hall elements in the sensing circuit 2, the switching circuit 6a and the externally equipped charging circuit 7a constitute so-called externally equipped circuits which are normally arranged outside the IC.
The externally equipped charging circuit 7a serves as a charging circuit for a capacitor C1 and is constituted by a resistor R1, a variable resistor VR and the capacitor C1 connected in series in this order between the power source line Vcc and the ground line GND. The charging circuit 7a adjusts the building-up time of a charging voltage (of which voltage signal is indicated by letter C in the drawing) by selecting the charging time constant with respect to the capacitor C1 through manipulation of the variable resistor VR. The dis which discharges charges in the capacitor C1 and resets the charged voltage to the ground level through the discharging operation.
The reference voltage generating circuit 7f is a resistor type divider circuit constituted by resistors R2 and R3 connected in series in this order between the power source line Vcc and the reference voltage setting circuit 7e, and is grounded via the reference voltage setting circuit 7e. A predetermined reference voltage (which voltage signal is indicated by letter D in the drawing) is generated at the node between the resistors R2 and R3.
The comparator 7d receives the changed voltage signal C and the reference voltage signal D and compares the magnitude of these signal voltages. As a result of the comparison, the comparator 7d outputs a detection signal E at the moment when the charge voltage signal C exceeds the reference voltage signal D.
The flip-flop 7b is set upon receipt of a reference rotary position pulse B (hereinafter called a reference pulse), which is generated in response to a reference rotary point, and is reset when the detection signal E is received. The flip-flop 7b further outputs an index signal F from the Q output terminal. In the present example, one of the signals from the Hall elements in the motor control circuit (in the drawing, the signal amplified by the input amplifying circuit 3 is used) is inputted to a pulse circuit 7g, wherein pulses with a narrow width are generated at the timing representing the reference rotary point in synchronism with, for example, the zero crossing point of a sinusoidal waveform signal or the building-up or falling-down timing of a rectangular waveform signal waveshaped from the sinusoidal waveform signal. Alternatively, these timings and these pulses are used as the reference pulse B. Further, the reference pulse B can be obtained by detecting the rotating condition of the motor 1 separately with a dedicated Hall element or photo sensor, and by converting the detected signal into a pulse form through the pulse circuit 7g.
Hereinafter, the operation for generating the index signal F in the index signal generating circuit 7 is explained with reference to the signal waveform diagram shown in FIG. 3.
Now, assuming that the connection of the switching circuit 6a is selected toward the power source line Vcc through the manipulation from the outside, and the selection signal generating circuit 6b is generating a signal of "H", the drive signal producing circuit 4 receives the speed selection signal A, and the rotating speed of the motor 1 is set at a rotating speed V1. At this instance, the time required to rotate from the reference rotary position through a predetermined rotating angle W with the present speed V1 is assumed as T1, which is determined so as to correspond to the pulse width of the index signal. Herein, the resistance value of the variable resistor VR is adjusted beforehand so that the above corresponding relationship is maintained.
When the reference pulses B are generated in association with the rotation of the motor 1, the flip-flop 7b is set upon receipt of the reference pulse B and the Q terminal is rendered "H", whereby an index signal F of "H" is generated in response to the generation of the reference pulse B. At the same time, the discharge circuit 7c receives an inverted signal *F of the index signal F from the Q output terminal of the flip-flop 7b to prevent discharge of the capacitor C1. Thereby, the externally equipped charging circuit 7a begins charging of the capacitor C1. As a result, the charging voltage signal C builds, up along the solid line Ca (see FIG. 3). The amplitude of the charge voltage signal C exceeds a reference amplitude Da of the reference voltage signal D at the moment when the time T1 determined by the adjustment of the variable resistor VR has passed.
At the moment of the exceeding, the comparator 7d outputs the detection signal E. Upon receipt of the same the flip-flop 7b is reset. Thereby, the index signal F is rendered "L" to terminate the above operation. Then, the charges on the capacitor C1 is discharged via the discharge circuit 7c. In such a way, an index signal F having a pulse width corresponding to the time T1 is outputted from the flip-flop 7b in synchronism with the reference pulse B.
When the connection of the switching circuit 6a is selected toward the ground line side GND, the selection signal generating circuit 6b generates a signal of "L", and with this speed selection signal A the rotating speed of the motor 1 is set at a rotating speed V2 faster than the rotating speed V1. The time required to rotate the same angle of W with the rotating speed V2 is thus assumed as T2, and at this time the resistance value of the variable resistor VR is also adjusted so that the pulse width of the index signal F corresponds to the time T2 (it is assumed herein that such adjustment is already completed).
When the reference pulses B are outputted in association with the rotation of the motor 1, the flip-flop 7b is set upon receipt of the same in the same manner as above. The index signal F is rendered "H" and at the same time, the discharge circuit 7c prevents the discharge of the capacitor C1 upon receipt of the inverted signal *F of the index signal F. Thus the externally equipped charging circuit 7a begins charging and at this time the charge voltage signal C builds-up along the dotted line Cb. Since the pulse width of the index signal is already adjusted to the time T2, the amplitude of the charge voltage signal C exceeds the predetermined amplitude Da of the reference voltage signal D at the moment when the time T2 has passed.
At this moment, the comparator 7d outputs a detection signal E. Upon receipt of the same the flip-flop 7b is reset and the index signal F is rendered "L". As a result, the charge on the capacitor C1 is discharged via the discharge circuit 7c. In such a way, the index signal F having the width T2 is outputted starting in synchronism with the reference pulse B, and both the previous index signal F and the present index signal F are equally generated for the period corresponding to the motor rotating angle W.
As explained above, with the index signal generating circuit in the conventional motor control circuit for an FDD, when the rotating speed of the motor 1 is set at one of different rotating speeds V1 and V2 by the speed selection signal, the resistance value of the variable resistor VR in the externally equipped charge circuit 7a has to be adjusted so that the pulse width of the index signal corresponds to the time period required to rotate through the predetermined angle W in response to the selected rotating speed.
Therefore, when one of a plurality of rotating speeds such as 300, 360 and 600 rpm is required to be selected as a rotating speed for an FDD, readjustment work for setting the pulse width of the index signal which is indispensable in connection with the selection or switching of the rotating speed and an additional line for the readjustment work have been needed.